The present invention related to LED traffic signals. More particularly, it relates to an intelligent self-diagnosing traffic signal that identifies the end of the useful life of the signal.
1. Field of the Invention
2. Description of Related Art
Light Emitting Diodes (LEDs) traffic signals usage is wide spread. LEDs offer interesting advantages over incandescent lights. Those advantages include, for example, low power consumption and long life.
While LEDs last for a very long time (typical meantime between failure or MTBF is in the millions of hours), their light output intensity degrades over time. Manufacturers generally warranty their LED products for a certain period of time (typically 5 years). Depending on the operating conditions, including ambient temperature and signal duty cycle, the signal light output might be satisfactory for a period exceeding the warranty period. Users would like to use the LED signal until it reaches the end of its useful life; however because faulty traffic signals can result in an unsafe road condition, signals are required to have sufficient light output. One approach is to replace all signals upon warranty expiration. However, this results in signals being replaced while there is still significant useful life left in them. Another approach is to have the lamp measured in a lab at and/or after warranty expiration to assess the signal's condition. This only provides information at a particular moment in time and does not provide on-going data about the condition of the lamp. There is a need for an intellig3ent self-diagnosing traffic signal that allows users to make use of the long life of the LEDs without compromising safety.
U.S. application Ser. No. 10/762,743 is herein incorporated in its entirety. The LED signal has a communication link with a traffic controller. It receives commands and provides feedback information to the traffic controller. In the present invention, the signal is a stand-alone system. The traffic controller feeds voltage, but the signal does not have any additional interface with it.
U.S. Pat. No. 6,667,623 is also incorporated in its entirety. A system to monitor light output degradation is disclosed. The invention in U.S. Pat. No. 6,667,623 uses a light sensor to detect end of life. The proposed invention compiles a database of the various parameters (temperature, hours of operation, light output etc) in order to more accurately assess the signal's end of life and adjust the LED current to extend the signal's life.
A prior art method to change the LED current in response to a sensor's output uses a variable load in parallel with the LEDs. In the present invention, there is no variable load; current is directly adjusted by the power supply. One prior art signal utilizes a compensation circuit based on light output feedback from a photosensor. The present invention uses the photosensor feedback primarily in order to detect end of life of the signal and to compensate light output by increasing LED current as long as it is in the permissible range in order to extend the signal's life. The present invention also has communication capabilities.
An alternative prior art method senses the light output of an extra LED and adjusting the power supply according to the light output generated by the extra LED. The present invention measures the light output for the complete array, calculates the number of hours of operation and determine end of life.
A prior art system predicts when light output will fall under predetermined threshold. The present invention does not predict but actually shuts down the signals or send an EOL signal when the signal has reached the end of its useful life.